1. Field of the Invention
The invention relates to fluid delivery systems. In particular, the invention relates to new and useful improvements in an apparatus for delivering injectate to patients in medical applications.
2. Discussion of the Prior Art
In various medical contexts, it is important to be able to control the delivery of an injectate fluid to a patient. In one particular medical procedure, known as bolus thermodilution, it is particularly important to accurately monitor the temperature of the injectate as it enters the patient in order to accurately calculate the patient's cardiac output. This well known technique for measuring cardiac output is disclosed in U.S. Pat. No. 4,508,123, to Wyatt et al., which has been assigned to the predecessor of the current assignee, the entire disclosure of which is incorporated herein by this reference.
As discussed in the prior art system of Wyatt et al., a thermodilution injectate assembly includes a length of flexible tubing with a catheter attached thereto for introducing fluid to the patient, an insulated container for cooling the fluid, a temperature probe at the proximal end of the catheter, a temperature probe at the distal end of the catheter, a syringe, and a three-ported stopcock in fluid communication with the fluid container, the flexible tubing and the syringe. The syringe is utilized to draw cooled fluid from the container and inject the fluid through the flexible tubing into the patient. The stopcock is utilized to create a flow through path either between the syringe and the container, or between the syringe and the flexible tubing. The first temperature probe is used to measure the temperature of the injectate as it enters the patient and the second temperature probe is used to measure downstream temperature. The change in fluid temperature is used to calculate cardiac output according to well known principles, as described in Wyatt et al.
One disadvantage of the system of Wyatt et al., is the need for the three-way stopcock. The operator of the system must first manually turn the stopcock to a first position to permit fluid to fill the syringe and then manually turn the stopcock to a second position to permit fluid flow from the syringe into the patient.
In an improved prior art system utilized by the applicant's assignee, Baxter International Inc., a dual directional check valve assembly is utilized in place of the stopcock of Wyatt et al. Such a check valve assembly is disclosed in U.S. Pat. No. 4,210,173, to Choksi et al., which has been assigned to the predecessor of the current assignee, the entire disclosure of which is incorporated herein by this reference. As disclosed therein, flexible, resilient discs are placed on opposite ends of flexible tubing between the fluid inlet and the fluid outlet respectively.
The use of the Choksi et al. assembly with the Wyatt et al. system permits the syringe to withdraw injectate from the container during its withdrawal stroke and inject it into the patient during its injectate stroke, without the need for a stopcock. During the syringe withdrawal stroke, the check valve between the fluid container and the syringe is opened and the check valve between the syringe and the outlet is closed. During the syringe injection stroke, the check valves are in the opposite configuration.
In this improved system, the check valve assembly is an integral unit which is connectable at its distal end, via a flow-through fitting, to the proximal end of the catheter. The proximal end of the assembly has two ports, one which is connectable to the injectate source and one which is connectable to the syringe. In this system, the temperature probe is placed just distal to the flow-through fitting at the proximal end of the catheter tubing.
The aforementioned system has many disadvantages, among which are the number of tubing connections, the number of fluid connections, the difficulty in handling, and the increased manufacturing cost.
Accordingly, it is an object of the invention to provide an efficiently designed integral flow through injectate assembly.
Further objects of the invention are to provide a flow through injectate assembly that is easy and inexpensive to manufacture, that is easy to handle and that has less flow path connections.
Yet a further object of the invention is to provide a flow through injectate assembly that permits accurate sensing of the injectate flowing therethrough.